Many electronic consumer products today utilize some type of electronic display. This display may offer almost any type of numerical or graphical information to the user relating to status and/or mode of operation of the electronic device. Depending on the type of display that is to be used, there are many types of technologies available for driving the display in order to display the required information. As seen in prior art system 100 of FIG. 1, a microprocessor 101 is used with a display driver 103 and resister network 105 to drive i.e. supply information to the LCD display 107.
One such LCD display is a twisted nematic (TN) display. The TN display is commonly used because it is capable of displaying a moderate amount of information to the user while still maintaining low cost with minimal implementation effort. In order to optimize display functionality, a number of low cost liquid crystal display solutions have been developed for use with the TN display using Pulse Width Modulation (PWM). These techniques utilize a driving scheme that enables a multiple character TN display to be incorporated into an electronic device using a limited number of control lines from an associated microprocessor. This type of scheme eliminates the need for all external components and thus can greatly reduce the manufacturing cost of the display.
For example, a standard liquid crystal display multiplex (LCD MUX) drive operates by addressing/selecting a single row of the LCD at a time. After this selection, the desired ON/OFF states are applied to that selected row through the LCD columns which are common to all ROWs. Rows are selected in a continuing round-robin fashion. Only when a row is addressed/selected, do the states on the columns affect a row, otherwise on unselected rows, the column states are seen as low level noise. Therefore, Table 1 shows each row supplied with the following type of waveform:
TABLE 1 ______________________________________ Row selected Column 1 Column x ______________________________________ unselected low level noise low level noise selected significant on/off info significant on/off info unselected low level noise low level noise unselected low level noise low level noise ______________________________________
As is evident to those skilled in the art, time division is being used to select one row at a time. The method of selecting the row is by supplying the row selected with voltage amplitude several times the level of unselected rows. The method of selecting the row is therefore voltage division multiplexing.
Voltage division multiplexing is a technique requiring more than two driven voltage levels. This technique is not possible with digital circuitry since digital circuitry by definition is limited to two voltage levels. Thus, in modern day electronic equipment that includes an multiplexed LCD display, some type of analog circuitry is required to interface the multiplexed LCD to the equipment's control circuits. In general, digital circuits are smaller and less costly than analog circuits for similar functions, and therefore an all digital multiplexed LCD drive scheme would be of smaller size and less costly to implement than an analog multiplexed LCD drive scheme.
Accordingly, the need exists for a digital drive scheme for an LCD multiplexed display that can be used with electronic devices and circuits having easy implementation and low cost.